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The Architecture and Connective Potential of Blowout Wings in Fluvio-Deltaic Environments

Abstract

Fluvio-lacustrine systems are prone to experiencing significant flood events separated by longer low energy periods. During low flow, sediment is stored upstream of the lake as mid channel and side attached bars. During high-discharge events, water level rises above the topographically low delta front levees, the turbulent jet of the river is positioned upstream of the levee terminus where levees are less confining, and the previously stored sediment is flushed from the channel into the lake basin laterally as sheets. This process forms a laterally extensive, well sorted wedge shaped deposit of fine grained sand called a blowout wing (after Tomanka, 2013). These wings are documented in the ancient within the Kayenta Formation, UT, where the sand wings demonstrated a significant increase in connectivity between statistically clustered fluvio-lacustrine channel belts. In this research, we document two examples of blowout wings forming in the modern. The first example is a lake sourced by a sandy, bedload dominated river (Red River, Lake Texoma, TX), and the second is a lake sourced by a mud dominated river (Denton Creek, Lake Grapevine, TX). Wings are composed of fine to medium grained, well sorted sand. The deposits are thin and laterally continuous, with measured thicknesses of 5-20 cm that thin away from channel axis. Wings have an aerial extent of several hundred meters, scaling to 4-6 times the channel width. The Red River at Lake Texoma has a channel width of 125m and deposits wings with an aerial extent of 250-350m long along the levee of the delta channel and 300-500m laterally. As the Red River has prograded into the basin, 5-6 individual blowout wings form a wing complex 1500m long and 500-600m laterally from the channel. Denton Creek at Lake Grapevine has a channel width of 25m and deposits wings on the order of 50-125m along the levee of the delta channel and 60-150m laterally. Three wings at Lake Grapevine form a wing complex 300m long and 100-150m laterally. The amalgamation and statistical clustering of fluvio-deltaic channel belts is increased by the presence of blowout wings, resulting in higher total reservoir size and connectivity. Blowout wings should be, and are, found in modern systems and subsequently the rock record recording fluvio-lacustrine environments of deposition.